OBJECTIVES: A. Morphogenesis and the basis for the transition of dimorphic fungi to the parasitic form. 1. Sequential events in the transition; 2. Control mechanism in the transition; 3. Purification of RNA polymerases from both phases of H. capsulatum. B. Use of murine leukemias and lymphomas to set up models of opportunistic infections. BIBLIOGRAPHIC REFERENCES: Cheung, S.C., Medoff, G., Schlessinger, D. and Kobayashi, G.S. Response of yeast phases of Histoplasma capsulatum to amphotericin B and actinomycin D. Antimicrob. Ag. Chemother. 8:498, 1975. Cheung, S.C., Medoff, G., Schlessinger, D. and Kobayashi, G.S. Stability of amphotericin B in fungal culture media. Antimicrob. Ag. Chemother. 8:426, 1975.